The present invention relates to a reel assembly, in particular, a reel assembly for use in a capstan winch of the kind used to deploy and wind in cables used in underwater and seabed applications, for example, seismic cables.
Such capstan winches are used to de-tension seismic cables which, typically, make several turns around the capstan winch before passing to a storage winch. The capstan and storage winches are driven so as to maintain constant tension in the length of cable between the two winches.
The capstan winch also acts to align the cable with the storage winch downstream by, for example, centering the cable as it passes around the reel of the capstan winch. This involves exerting lateral forces on the cable while it is under tension, leading to twisting or, worse, damage to the cable. It is an object of the present invention to alleviate this problem.
In accordance with the invention, there is provided a reel assembly and a capstan winch incorporating a reel assembly, the reel assembly comprising a reel mounted for rotation and having a generally cylindrical surface onto which a cable can be wound and a pair of generally annular floating flange elements mounted for rotation with the reel, the flange elements being supported so that the planes in which they rotate converge towards one another; the generally cylindrical surface of the reel being provided with a plurality of alternating lands and grooves extending from one flange element to the other and the flange elements each having formed on a generally annular surface thereof which, in a respective direction of rotation, contacts a cable being wound onto the reel, a plurality of alternating inclined faces which correspond with the alternating lands and grooves on the generally cylindrical surface of the reel; the alternating inclined faces being so angled that the inclined faces formed on the two flange elements which correspond to each land formed on the reel are generally parallel to one another and the inclined faces formed on the two flange elements which correspond to each groove formed on the reel converge towards one another, so that substantial lateral forces are exerted on a cable being wound onto the reel only when the cable overlies the grooves formed on the reel.
Because the floating flange elements exert a lateral force on the cable substantially only when it is overlying the grooves formed in the reel, friction between the cable and the reel is reduced, allowing the cable to slide sideways more easily. Thus the risk of damage to the cable is reduced.
Conveniently, the flange elements converge towards each other symmetrically with respect to a plane perpendicular to the axis of rotation of the reel.
In a preferred embodiment of the invention, said plurality of inclined faces is formed by a plurality of smoothly curved elements detachably secured around the annular face of each flange element, and said plurality of lands and grooves is formed by a plurality of curved sections detachably secured around the cylindrical surface of the reel.